How do I impersonate a user? I can't find any documentation that explains how to do this or even hint that it's possible.

Use case: I perform administrative tasks like assign grants and roles to catalogs, schemas, and tables for the benefit of business users. Afterwards, I want to see what the user would see when they login. Currently, I must wait for the user to get back to me - which could be days. in the meantime, I've already changed directions numerous times and forgotten about their initial request.